Lung recruitment in mechanical ventilation

ABSTRACT

A ventilation system includes a breathing apparatus which provides a mechanical ventilation to a patient. The breathing apparatus is configured to perform an automated full recruitment manoeuvre, FRM, comprising a recruitment phase and a PEEP titration phase, wherein the PEEP titration phase is a phase of stepwise decrease in PEEP from a maximum PEEP level to a minimum PEEP level, via one or more intermediate PEEP levels. The breathing apparatus is configured to deliver a number of breaths at each PEEP level, and to monitor a parameter indicative of a potentially harmful level of ventilation during the PEEP titration. The breathing apparatus is further configured to automatically decrease PEEP to a lower PEEP level when the monitored parameter reaches a first threshold value.

TECHNICAL FIELD

The present disclosure relates to the field of lung recruitment duringmechanical ventilation and, in particular, to a ventilation system, amethod, and a computer program for lung recruitment in mechanicallyventilated patients.

BACKGROUND

Lung recruitment manoeuvres (RM) have gained attention over the pastyears to overcome lung collapse (atelectasis) and improve lung functionin order to decrease the risk of developing ventilator induced lunginjury (VILI) in mechanically ventilated patients suffering from AcuteRespiratory Distress Syndrome (ARDS).

A poorly aerated lung with areas of collapsed alveoli will lead to poorventilation of the patient, requiring higher driving pressures and FiO₂settings to get adequate oxygenation of the patient. The recurringopening and collapse of alveoli during these conditions contributes tothe risk of exacerbated lung injury with an increased risk of prolongedhospitalisation and mortality.

By applying a lung protective strategy through re-recruiting collapsedlung tissue and applying an appropriate end-expiratory pressure (PEEP)in order to sustain an open lung, the lung function is improved andmorbidity in mechanically ventilated patients may be substantiallyreduced.

The literature describes different types of lung recruitment manoeuvers,where the simplest ones include sustained inflation at a fixed pressurefor a fixed time interval, e.g. 40 cmH₂O for 40 seconds, or a slowgradual increase in airway pressure through a constant flow for a singleinflation/deflation cycle. Another lung recruitment strategy that hasbeen proved successful is a stepwise manoeuvre where PEEP and peakpressure is first increased over a number of breaths until a pressureplateau is maintained for up to two minutes, followed by a PEEPtitration phase where an optimal PEEP is identified to achieve a volumetarget for the patient.

Such a stepwise lung recruitment manoeuvre is described in U.S. Pat. No.9,173,595. According to the recruitment manoeuvre disclosed in U.S. Pat.No. 9,173,595, data samples of gas concentration of expired gas are usedto calculate tracing values that are sensitive to changes of alveolardead space, whereby the tracing values are used to determine an optimalPEEP during the PEEP titration phase.

Another stepwise and at least partly automated lung recruitment strategyis disclosed in WO 2012/139159. According to the recruitment strategydisclosed in WO 2012/139159, the compliance of the patient's respiratorysystem is analysed to find an optimal PEEP during the PEEP titrationphase.

There are several challenges associated with automation of lungrecruitment manoeuvres. Some challenges relate to the handling of thehigh and potentially harmful pressures and flows required for effectivelung recruitment. Other challenges relate to the optimisation ofventilation settings during and after the lung recruitment manoeuvre.Yet other challenges relate to the complexity of configuration andinitiation of the lung recruitment manoeuvre.

SUMMARY

It is an objective of the disclosure to address one or more of the abovementioned challenges.

It is a particular objective of the disclosure to present an automatedrecruitment manoeuvre that minimises potentially adverse effects of thelung recruitment manoeuvre on the lungs of the ventilated patient.

These and other objectives are achieved in accordance with the presentdisclosure by a system, a method, and a computer program as defined bythe appended claims.

According to an aspect of the disclosure, there is provided aventilation system comprising a breathing apparatus for providingmechanical ventilation to a patient. The breathing apparatus isconfigured to perform an automated full recruitment manoeuvre, FRM,comprising a recruitment phase and a PEEP titration phase, wherein thePEEP titration phase is a phase of stepwise decrease in PEEP from amaximum PEEP level to a minimum PEEP level, via one or more intermediatePEEP levels. The breathing apparatus is configured to deliver a numberof breaths to the patient at each PEEP level, and to monitor a parameterindicative of a potentially harmful level of ventilation during the PEEPtitration. The breathing apparatus is further configured toautomatically decrease PEEP to a lower PEEP level, e.g. to the nextlower PEEP level, when the monitored parameter reaches a first thresholdvalue.

This has the effect of avoiding potentially harmful levels ofventilation during PEEP titration and so minimises potentially adverseeffects of the lung recruitment manoeuvre on the lungs of the ventilatedpatient.

The problem of potentially harmful levels of ventilations during lungrecruitment is particularly relevant when PEEP titration is carried outin a volume-controlled (VC) mode where the airway pressure of theventilated patient cannot be directly controlled. In particular duringthe initial PEEP steps of the PEEP titration staircase, there is a riskthat a set tidal volume for PEEP titration results in high airwaypressures due to the typically non-compliant lung of the patient at therelatively high PEEP levels. In this case, potentially harmful levels ofairway pressure can be avoided by monitoring a parameter indicative of arespiratory pressure of the patient, such as the airway pressure, andautomatically reducing PEEP to a lower PEEP level when the monitoredrespiratory pressure exceeds a first threshold value.

That the breathing apparatus is configured to lower the PEEP to a lowerPEEP level when the monitored parameter reaches the first thresholdvalue means that the breathing apparatus is configured to abort deliveryof breaths on the current PEEP step upon detection of the crossing ofthe monitored parameter of the first threshold value, and to reduce PEEPto the lower PEEP level for subsequent breaths. The breathing apparatusis typically configured to reduce PEEP as soon as possible upondetection of the crossing of the monitored parameter of the firstthreshold value. Preferably, the breathing apparatus is configured toreduce PEEP to the lower level within at least three breaths fromdetection of the crossing of the monitored parameter of the firstthreshold value.

In some embodiments, the breathing apparatus is configured to decreasePEEP to a lower PEEP level only when the monitored parameter reaches thefirst threshold value at least for a second time on a current PEEPlevel. This is advantageous in that the PEEP level is not reduced if thecrossing of the first threshold value is caused by an occasional event,such as patient coughing or external manipulation of the patient, ratherthan a potentially harmful level of ventilation. The purpose of the PEEPtitration phase is to identify an optimal PEEP of the patient, and thechances of reliably determining the optimal PEEP of the patient areimproved if ventilation on the respective PEEP steps of the PEEPtitration staircase is not prematurely aborted.

In some embodiments, the breathing apparatus is configured to decreasePEEP to a lower PEEP level when the monitored parameter reaches thefirst threshold value for a first time on a current PEEP level only ifthe monitored parameter has reached the first threshold value duringventilation on any of the preceding PEEP levels. This also has theeffect of avoiding premature reduction of PEEP not caused by potentiallyharmful ventilation of the patient. If the monitored parameter hasreached the first threshold value also on previous (higher) PEEP steps,it can be assumed that the threshold is reached due to a potentiallyharmful level of ventilation, wherefore the PEEP level should bereduced. If, on the other hand, the first threshold value has not beenreached on previous (higher) PEEP steps, it can be assumed that thethreshold is reached due to an occasional event not related topotentially harmful levels of ventilation, such as patient coughing orexternal manipulation of the patient, wherefore a reduction in PEEP isnot required. In this case, the breathing apparatus may still beconfigured to decrease PEEP to a lower PEEP level when the monitoredparameter reaches the first threshold value for at least a second timeon a current PEEP level. This has the effect of ensuring that PEEP isreduced if the crossing of the first threshold value is likely to becaused by a too high level of ventilation.

The ventilation system may further be configured to determine if themonitored parameter reaches a second threshold value being lower thanthe first threshold value during at least two consecutive breaths, andto decrease PEEP to a lower PEEP level if the monitored parameterreaches the second threshold value during at least two consecutivebreaths. In some situations, in particular during the initial steps ofPEEP titration in VC mode, the airway pressure of the patient may behigh enough to have potential detrimental effect on the patient's lungsdue to over distension of the lung tissue, yet not high enough to reachthe first threshold value. By employing a second threshold value forconsecutive breaths, which second threshold value is lower than thefirst threshold value for single breaths, the PEEP will be automaticallyreduced also in these situations.

According to another aspect of the present disclosure, there is provideda method for lung recruitment in a patient (3) being mechanicallyventilated by a breathing apparatus (2), comprising the steps of:

-   -   performing (S91) an FRM manoeuvre comprising a recruitment phase        and a PEEP titration phase, wherein the PEEP titration phase is        a phase of stepwise decrease in PEEP from a maximum PEEP level        to a minimum PEEP level, via one or more intermediate PEEP        levels;    -   delivering (S92) a number of breaths at each PEEP level;    -   monitoring (S93) a parameter indicative of a potentially harmful        level of ventilation during the PEEP titration, and    -   automatically decreasing PEEP to a lower PEEP level when the        monitored parameter reaches a first threshold value.

In some embodiments, PEEP may be decreased to a lower PEEP level onlywhen the monitored parameter reaches the first threshold value at leastfor a second time on a current PEEP level.

In some embodiments, PEEP may be decreased to a lower PEEP level whenthe monitored parameter reaches the first threshold value for a firsttime on a current PEEP level only if the monitored parameter has reachedthe first threshold value during ventilation on any of the precedingPEEP levels. In this case, PEEP may still be decreased to a lower PEEPlevel when the monitored parameter reaches the first threshold value forat least a second time on a current PEEP level.

The method may further comprise the steps of determining if themonitored parameter has reached a second threshold value being lowerthan the first threshold value during at least two consecutive breaths,and decreasing PEEP to a lower PEEP level if the monitored parameter hasreached the second threshold value during at least two consecutivebreaths.

The monitored parameter may be any parameter indicative of a potentiallyharmful level of ventilation of the patient. In some embodiments, theparameter is indicative of a respiratory pressure of the patient, suchas an airway pressure.

The method is typically a computer-implemented method performed by thebreathing apparatus upon execution of a computer program for lungrecruitment of a mechanically ventilated patient. The computer programcomprises computer-readable instructions which, when executed by acomputer, causes the breathing apparatus to perform any of, or anycombination of, the above described method steps.

The computer program may be stored in a non-volatile memory of thebreathing apparatus, e.g. in a non-volatile memory hardware device.

The proposed method may be performed using standard hardware of astate-of-the-art breathing apparatus. Consequently, installation of thecomputer program on existing breathing apparatuses may allow existingbreathing apparatuses to perform the proposed method without hardwaremodification.

More advantageous aspects of the proposed ventilation system, method andcomputer program will be described in the detailed description ofembodiments following hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description provided hereinafter and the accompanying drawingswhich are given by way of illustration only. In the different drawings,same reference numerals correspond to the same element.

FIG. 1 illustrates an exemplary embodiment of a mechanical ventilationsystem for performing an automated recruitment manoeuvre in accordancewith an exemplary embodiment of the disclosure.

FIG. 2 illustrates pressure trajectories for PEEP and PIP during a fullrecruitment manoeuvre, FRM.

FIG. 3 illustrates pressure trajectories for PEEP and PIP during a quickrecruitment manoeuvre, QRM.

FIG. 4 illustrates an exemplary GUI view for planning an automated FRMmanoeuvre.

FIG. 5 illustrates an exemplary GUI view for monitoring an automated FRMmanoeuvre.

FIG. 6 illustrates an exemplary GUI view for evaluating an automated FRMmanoeuvre.

FIG. 7 illustrates an exemplary GUI view for planning an automated QRMmanoeuvre.

FIG. 8 illustrates an exemplary GUI view for monitoring an automated QRMmanoeuvre.

FIG. 9 is a flowchart illustrating a method for lung recruitment of amechanically ventilated patient, according to an exemplary embodiment ofthe disclosure.

DETAILED DESCRIPTION

The present disclosure relates to an automated lung recruitmentmanoeuvre for re-opening collapsed alveoli in a mechanically ventilatedpatient. The recruitment manoeuvre may be automatically performed by abreathing apparatus providing the mechanical ventilation to the patient.The recruitment manoeuvre may be fully implemented in software, thusallowing a conventionally equipped breathing apparatus to perform themanoeuvre with no modification of existing hardware.

FIG. 1 illustrates an exemplary embodiment of a mechanical ventilationsystem 1 comprising a breathing apparatus 2 configured to perform anautomated recruitment manoeuvre in accordance with the principlesdisclosed herein. The breathing apparatus 2 may be any type of apparatuscapable of providing mechanical ventilation to the patient 3 through thesupply of pressurised breathing gas to the airways of the patient 3.Ventilators and anaesthesia machines are non-limiting examples of suchbreathing apparatuses.

The breathing apparatus 2 is connected to the patient 3 via a patientcircuit comprising an inspiratory line 5 for supplying breathing gas tothe patient 3, and an expiratory line 7 for conveying expiration gasaway from the patient 3. The inspiratory line 5 and the expiratory line7 are connected to the patient 3 via a patient connector 13, such as anendotracheal tube. The inspiratory line 5 and the expiratory line 7 maybe connected to the patient connector either directly (if using doublelumen tubing) or via a Y-piece. In the illustrated example, theinspiratory line 5 and the expiratory line 7 are connected to a commonline 9 via a Y-piece 11, which common line is connected to the patient 3via the patient connector 13.

The breathing apparatus 2 comprises a control unit or control computer15 for controlling the ventilation of the patient 3 based on pre-setparameters and/or measurements obtained by various sensors of thebreathing apparatus. The control computer 15 controls the ventilation ofthe patient 3 by controlling a pneumatic unit 17 of the breathingapparatus 2, which pneumatic unit 17 is connected on one hand to one ormore gas sources 19, 21 and on the other hand to the inspiratory line 5for regulating a flow and/or pressure of breathing gas delivered to thepatient 3. The pneumatic unit 17 may comprise various gas mixing andregulating means well known in the art of ventilation, such as gasmixing chambers, controllable gas mixing valves, turbines, controllableinspiration and/or expiration valves, etc.

The ventilation system 1 further comprises one or more flow sensors 23,23′, 23″ for measuring respiratory flow, and one or more pressuresensors 25, 25′, 25″ for measuring respiratory pressure. The flow sensor23 may be a proximal flow sensor located close to the patient 3 (e.g. inor close to the Y-piece 11) and configured to measure both aninspiratory flow of breathing gas delivered towards the patient 3 duringinspiration, and an expiratory flow of gas exhaled by the patient 3during expiration. Likewise, the pressure sensor 25 may be a proximalpressure sensor located close to the patient 3 (e.g. in or close to theY-piece 11) and configured to measure, during both inspiration andexpiration, a proximate patient pressure substantially corresponding toan airway pressure of the patient 3. Alternatively or in addition to theflow sensor 23 and the pressure sensor 25 disposed in the Y-piece 11 ofthe patient circuit, the breathing apparatus 2 may comprise one or moreinternal flow sensors for measuring respiratory gas flow, and/or one ormore internal pressure sensors for measuring respiratory gas pressure.For example, the breathing apparatus 2 may comprise a flow sensor 23′for measuring a flow of breathing gas in an inspiratory flow channel ofthe breathing apparatus 2, and/or a pressure sensor 25′ for measuring agas pressure in the inspiratory flow channel of the breathing apparatus.Alternatively, or in addition, the breathing apparatus 2 may comprise aflow sensor 23″ for measuring a flow of expiration gas in an expiratoryflow channel of the breathing apparatus 2, and/or a pressure sensor 25″for measuring a gas pressure in the expiratory flow channel of thebreathing apparatus.

The measurement signals obtained by the one or more flow sensors 23,23′, 23″ and the one or more pressure sensors 25, 25′, 25″ aretransmitted to the control computer 15, whereby the control computer 15can control the flow and volume of breathing gas delivered to thepatient 3, as well as the airway pressure of the patient 3, bycontrolling the pneumatic unit 17 based on the measurement signals. Inthis exemplary embodiment, the pneumatic unit 17 comprises acontrollable inspiratory valve 27 for regulating inspiratory flow andpressure, and a controllable expiratory valve 29 for controlling anexpiratory pressure applied to the patient 3 during expiration.

The control computer 15 comprises a processor or processing unit 30 anda non-volatile memory hardware device 31 storing one or more computerprograms for controlling the operation of the breathing apparatus 2,including a computer program for lung recruitment comprisinginstructions for carrying out an automated lung recruitment manoeuvre inaccordance with the principles described herein. Unless statedotherwise, actions and method steps described hereinafter are performedby, or caused by, the control computer 15 of the breathing apparatus 2upon execution by the processing unit 30 of different code segments ofthe computer program for lung recruitment, stored in the memory 31. Thecomputer program further comprises functionality for configuring,initiating, monitoring and evaluating the automated lung recruitmentmanoeuvre. This functionality will hereinafter be referred to as theOpen Lung Tool (OLT) of the breathing apparatus 3.

The automated lung recruitment manoeuvre and the OLT tool of thebreathing apparatus 2 will now be described with reference made to FIGS.1-8.

In general, in order to ensure sufficient gas exchange within the lungsof the patient 3, the tidal volume must be sufficiently large. The tidalvolume of the ventilated patient depends on the pressure applied to theairways of the patient and the compliance of the patient's lungs.Therefore, a certain pressure swing between a pressure applied to thepatient at the start of inspiration (typically corresponding to apositive end-expiratory pressure, PEEP, of the preceding expiration) anda peak inspiratory pressure, PIP, (in many cases corresponding to anend-inspiratory pressure, EIP), is required in order to achieve asufficient tidal volume. Besides re-opening of collapsed alveoli, theaim of the lung recruitment manoeuvre is to find a setting for PEEPwhich is high enough to prevent re-collapse of recruited alveoli whilebeing low enough to allow for sufficient tidal volumes at relatively lowinspiratory peak pressures.

Reference will now be made to FIGS. 2 and 3, illustrating exemplaryembodiments of two different types of lung recruitment manoeuvres thatmay be automatically performed by the breathing apparatus 2 in FIG. 1.

FIG. 2 illustrates a full recruitment manoeuvre (FRM) comprising arecruitment phase, a PEEP titration phase and an optional re-recruitmentphase following the PEEP titration phase. An FRM is typically performedwhen the patient 3 has not been subjected to any previous lungrecruitment manoeuvre and there is no previous knowledge on the lungdynamics of the patient, or when there is reasons to believe that thelung dynamics of the patient have changed since a previously performedFRM, e.g. after changes in the position or the overall physiologicalstate of the patient.

FIG. 3 illustrates a quick recruitment phase (QRM) comprising arecruitment phase without subsequent PEEP titration or re-recruitmentphases. A QRM may be advantageously performed in situations where theoptimal PEEP level is known beforehand (e.g. from a previous FRM) andwhere substantial changes in the lung dynamics of the patient is notanticipated. The primary intention with the QRM manoeuvre is to providea standardised and safe way of recruiting alveoli that have collapseddue to temporary disconnection of the patient 3 from the breathingapparatus 2, e.g. after patient transportation or suctioning procedures.QRM may also be advantageously used instead of FRM for healthy patientsnot suffering from severe lung injuries, where a perfect adaption ofventilator settings to the lung dynamics of the patient is less crucial.

The recruitment phase of both the FRM and QRM manoeuvres involves anincrease in one or both of PIP and PEEP in order to open up closedalveoli. The increase may be a single-step increase in PIP and/or PEEPbut, more commonly, the increase is a gradual increase in PIP and/orPEEP that is performed to gradually prepare the lungs for the relativelyhigh plateau pressures often required to open up closed alveoli. In theillustrated embodiments, the recruitment phase of both the FRM manoeuvreand the QRM manoeuvre is a phase of stepwise increase in both PEEP andPIP, from a respective minimum level to a respective maximum level.

The PEEP titration phase of the FRM manoeuvre is a phase of gradualdecrease in PEEP for identifying a PEEP level that is optimised to thelung dynamics of the patient following the recruitment phase. This PEEPlevel is herein referred to as optimal PEEP. Typically, the PEEPtitration phase is a phase of stepwise decrease in both PEEP and PIP,from a respective maximum level to a respective minimum level.

The purpose of the re-recruitment phase of the FRM manoeuvre is tore-open any alveoli collapsing during the PEEP titration phase, and inparticular during the last steps of the PEEP titration phase. Like therecruitment phase, the re-recruitment phase of the FRM manoeuvreinvolves an increase in one or both of PIP and PEEP in order to open upclosed alveoli. The increase may be a single-step increase in PIP and/orPEEP but, more commonly, the increase is a gradual increase in PIPand/or PEEP that is performed to gradually prepare the lungs for therelatively high plateau pressures often required to open up closedalveoli. In the illustrated embodiment, the re-recruitment phase of theFRM manoeuvre is a phase of stepwise increase in both PEEP and PIP, froma respective minimum level to a respective maximum level. Typically butnot necessarily, the number of breaths on each step of there-recruitment staircase and/or the number of steps in there-recruitment staircase is reduced in relation to the recruitmentstaircase.

Prior to performing any of the FRM or the QRM manoeuvres, the patient issubject to baseline ventilation using baseline ventilation settings. Thebaseline ventilation may be any type of ventilation and take manydifferent forms but is typically performed in a controlled mode ofventilation. The phase of baseline ventilation may be succeeded by anoptional pre-recruitment (pre-RM) phase immediately preceding therecruitment manoeuvre. The purpose of the pre-RM phase is to collectcomparison data to be used for evaluation of the recruitment manoeuvrethrough comparison with data collected during an optionalpost-recruitment (post-RM) phase following the recruitment manoeuvre. Inthe post-RM phase, the patient is ventilated with ventilation settingsthat at least to some extent are optimised to the changed lung dynamicsof the patient, caused by the recruitment manoeuvre. As mentioned above,the post-RM phase further involves collection of post-RM comparisondata, which post-RM comparison data is compared with the pre-RMcomparison data to evaluate the effect on the patient of the post-RMventilation with optimised ventilation settings. Evaluation dataindicative of the effect on the patient may be presented to the operatorin the post-RM phase, together with the optimised ventilation settingsused during the post-RM phase and suggested for use during new baselineventilation following the post-RM phase. If the operator acknowledgesthe suggested ventilation settings, the patient will be subject to newbaseline ventilation using the optimised ventilation settings. In thiscase, the FRM and QRM manoeuvres can be said to constitutesemi-automated manoeuvres only requiring the operator to acknowledge useof suggested ventilation settings for new baseline ventilation. Inalternative embodiments, the breathing apparatus 2 performing the FRM orQRM manoeuvre may be configured to automatically enter into new baselineventilation with optimised ventilation settings following the manoeuvre,in which case the manoeuvre can be said to be fully automated.

The Full Recruitment Manoeuvre—FRM

The exemplary FRM manoeuvre illustrated in FIG. 2 will now be describedin more detail with reference to FIGS. 4-6. The FRM manoeuvre and theprocedure for carrying out an FRM manoeuvre may include the followingphases:

-   -   1) A planning phase for planning the FRM manoeuvre by selecting        recruitment and PEEP titration settings;    -   2) A pre-RM phase involving collection of: comparison data        indicative of the situation prior to FRM;    -   3) A recruitment phase for opening up collapsed alveoli,        comprising        -   a. a recruitment pre-conditioning phase of stepwise increase            of PEEP and PIP to prepare lung for recruitment, and        -   b. a plateau recruitment phase involving a potentially            prolonged last step of the recruitment staircase;    -   4) A PEEP titration phase involving identification of a an        optimal PEEP of the patient;    -   5) A re-recruitment phase that is similar to the FRM recruitment        phase but typically shorter in duration, and    -   6) A post-RM phase involving ventilation with optimised        ventilation settings, including optimised PEEP determined during        the PEEP titration phase, with initial collection of comparison        data for comparison with pre-RM comparison data.        FRM: Planning Phase

The above mentioned OLT tool of the breathing apparatus 2 comprises auser interface, e.g. a graphical user interface presented on a display32 of the breathing apparatus 2 (see FIG. 1), through which a breathingapparatus operator may plan, initiate, monitor and evaluate the FRM andQRM manoeuvres, as further described below. Via the OLT interface, thebreathing apparatus operator may enter planning views with relevantsettings for configuring the FRM and QRM manoeuvres. An exemplary FRMplanning view 33 comprising user-adjustable FRM settings for configuringthe FRM manoeuvre is illustrated in FIG. 4. That a setting isuser-adjustable herein means that it may be modified by a user.

The FRM settings include settings for maximum PEEP (PEEP max), maximumPIP (PIP max), incremental increase in PEEP (PEEP incr/step),respiratory rate (Recruitment rate), breaths per PEEP step duringrecruitment (Breaths/step), breaths at maximum PEEP (Breaths at PEEPmax), starting PEEP for PEEP titration (PEEP start), tidal volume(VT/PBW) during PEEP titration, and breaths per PEEP step during PEEPtitration (Breaths/step). When not preceded by a previous FRM manoeuvre,the FRM settings are typically default settings initiated for therelevant patient category (e.g. based on bodyweight). If, however, anFRM or a QRM manoeuvre has previously been performed for the samepatient 3, the FRM settings may be initiated from the FRM or QRMsettings used for the previous FRM or QRM manoeuvre. That a setting isinitiated from another parameter (e.g. another setting), or initiatedbased on the other parameter, herein means that the setting is eitherset to a fixed and non-adjustable value, or that the setting (in case ofa user-adjustable setting) is set to an initial value that can beadjusted by the user, which value is determined based on the otherparameter.

As illustrated in FIG. 4, the FRM planning view 33 further comprises avisualisation 34 of the planned pressure trajectories for the FRMmanoeuvre with clear indications of important characteristics of themanoeuvre, such as manoeuvre duration and PEEP and inspiratory peakpressure levels. Should the breathing apparatus operator change any FRMsetting in the FRM planning view, the pressure trajectories of thevisualisation 34 are updated accordingly. In the pressure trajectoryvisualisation, the planned PIP trajectory is denoted by reference sign Aand the planned PEEP trajectory is denoted by reference sign B.

FRM: Pre-RM Phase

With reference again made to FIG. 2, prior to the pre-RM phase, thepatient receives baseline ventilation in a preferred ventilation modeusing preferred ventilation settings. Lung recruitment manoeuvres,including the proposed FRM and QRM manoeuvres, may cause severediscomfort to the patient and any spontaneous breathing efforts mayprevent the manoeuvres from being performed in a safe and reliablemanner. Therefore, FRM and QRM should be carried out in controlled modesof ventilation for patients having no or a minimum of spontaneousbreathing. The baseline ventilation preceding the recruitment manoeuvreis therefore typically also performed in a controlled mode ofventilation, such as a pressure-controlled (PC) mode or avolume-controlled (VC) mode.

Upon initiation of the FRM manoeuvre, e.g. by actuation of a button bythe operator, the breathing apparatus 2 enters the pre-RM phase in whichthe patient 3 is ventilated for a few breaths (typically around fivebreaths) using the ventilation mode and ventilation settings of thebaseline ventilation. During this period of the pre-RM phase,hereinafter referred to as the pre-RM data collection period, comparisondata to be compared with comparison data obtained after the recruitmentmanoeuvre is collected. As will be discussed later on, the collecteddata may for instance include information regarding a driving pressure(Pdrive) applied to the patient 3, a dynamic compliance (Cdyn) of thelungs of the patient, PEEP, PIP and the inspiratory tidal volume (VTi)of the patient.

The pre-RM data collection period is followed by a pre-RM PC periodcomprising a few breaths (typically around three) of baselineventilation in PC mode, meaning that the breathing apparatus 2 may haveto switch to PC mode if operated in any other controlled mode ofventilation during the baseline ventilation and the pre-RM datacollection period. If so, the breathing apparatus 2 may be configured toautomatically set a driving pressure for the pre-RM PC period resultingin a tidal volume corresponding to the tidal volume of the patient priorto switching to PC mode. The respiratory rate during the period of PCventilation may be set to correspond to a respiratory rate setting(Recruitment rate) in the FRM planning view 33, theinspiration-to-expiration ratio (I:E) may be set to 1:1, and any triggerconditions for the triggering of additional breaths in response tospontaneous breathing efforts may be deactivated. For example, theconventional pressure trigger condition for PC mode may be deactivatedby reducing the trigger sensitivity, e.g. by setting the trigger levelto −20 cmH20. This level of PC ventilation constitutes a base level ofthe FRM recruitment staircase.

Furthermore, in the pre-RM phase, the breathing apparatus 2automatically changes relevant alarm limits while other alarms may bepre-muted for the duration of the FRM manoeuvre. For example, thebreathing apparatus may be configured to auto-adjust alarm limits formaximum PEEP and maximum PIP based on the FRM settings PEEP max and PIPmax in the FRM planning view 33, and to pre-mute any alarm relating tominute ventilation and/or CO2 levels. Other alarms, such as an alarm forlow PEEP, may also be changed or muted for the duration of themanoeuvre, or parts of the manoeuvre.

FRM: Recruitment Phase

During the recruitment phase of the FRM manoeuvre, PEEP and PIP arestepwise (incrementally) increased up to a respective plateau pressurecorresponding to maximum PEEP and maximum PIP, as illustrated both inFIG. 2 and the visualisation 34 of the pressure trajectories in FIG. 4.In the illustrated example, although not required, changes in PEEP andPIP are made simultaneously. The size of each PEEP step, i.e. theincremental increase in PEEP, is determined by the step size setting(PEEP incr/step) in the FRM planning view 33. The size of each PIP stepis determined by the maximum PIP setting (PIP max) and the number ofsteps in the recruitment staircase (as determined by an initial valuefor PEEP, the PEEP max setting and the PEEP incr/step setting). Theincremental increase in PEEP for each step may, for instance, be in therange of 3-7 cmH2O. The number of breaths on each step of therecruitment staircase (i.e. on each PEEP level below maximum PEEP) andthe number of breaths on the plateau (i.e. on the maximum PEEP level)are also determined by a respective setting (Breaths/step and Breaths atPEEP max) in the FRM planning view 33, independently of each other. Thenumber of breaths at each step of the recruitment staircase may forinstance be in the range of 1-10 breaths. The number of breaths on therecruitment plateau may be the same as the number of breaths on eachstep of the recruitment staircase. Preferably, however, the number ofbreaths on the plateau exceeds the number of breaths on each step of thestaircase. For example, the number of breaths on the plateau may be inthe range of 3-30 breaths.

The recruitment phase starts by increasing PEEP and PIP to the firststep of the recruitment staircase, whereafter the breathing apparatus 2steps through the recruitment staircase up to the maximum PIP and PEEPlevels in accordance with the settings in the FRM planning view 33. Theincremental limb of the staircase constitutes a pre-conditioning phasemainly serving to gradually prepare the lungs of the patient 2 forventilation on the maximum PIP level, while the plateau of the staircaseconstitutes a lung-opening phase mainly serving the purpose of openingcollapsed alveoli through high pressure ventilation. Typically, somecollapsed alveoli will open-up also during the pre-conditioning phase ofthe recruitment, whereby the stepwise increase in PEEP serves to keepthese newly recruited alveoli open.

The breathing apparatus 2 may, in some embodiments, further beconfigured to determine an alveolar opening pressure during therecruitment phase. The alveolar opening pressure corresponds to apressure level at which most previously closed alveoli are re-opened.The alveolar opening pressure may be lower than the set maximum PIPlevel. There are different means and techniques for determining alveolaropening pressure during lung recruitment manoeuvres, and the breathingapparatus 3 may be devised and configured to use any means and techniqueknown in the art for determining the alveolar opening pressure of thepatient 2 during the recruitment phase. For example, the breathingapparatus 2 may comprise or be connected to a carbon dioxide (CO2)module for measuring CO2 in expiration gases exhaled by the patient 3,and to use the measured CO2 values to identify the alveolar openingpressure. The breathing apparatus 2 may, for instance, be configured tocompare CO2 measurements (e.g. measurements of end-tidal CO2, VTCO2)obtained at different PIP levels of the incremental limb of therecruitment staircase, and to determine the alveolar opening pressure asthe PIP level at which a substantial reduction in expired CO2 isdetected.

In some embodiments, the operator of the breathing apparatus 3 may begiven the option to bypass the remainder of the recruitment phase upondetection of an alveolar opening pressure that is lower than the setmaximum PIP pressure. This functionality may, for example, beimplemented by displaying a dialogue window on the display of thebreathing apparatus 2 upon detection of the alveolar opening pressure bythe breathing apparatus. The dialogue window may comprise information onthe detection of the alveolar opening pressure and allow the operator tobypass the remainder of the recruitment phase, e.g. by pressing a buttonin the dialogue window. Alternatively, the breathing apparatus 2 may beconfigured to automatically bypass the remainder of the recruitmentphase upon detection of the alveolar opening pressure. Upon bypass ofthe remainder of the recruitment phase, the breathing apparatus 2 may beconfigured to go directly to the PEEP titration phase.

FRM: PEEP Titration Phase

During the PEEP titration phase, the breathing apparatus 2 attempts todetermine the optimal PEEP. As well known in the art, there are manyways in which a more or less optimal PEEP level of a patient can beidentified during a PEEP titration procedure, and the present disclosureis not limited to any particular way of doing so.

Non-limiting examples of parameters that may be used by the breathingapparatus 2 to establish the optimal PEEP is the dynamic compliance ofthe patient, pressures indicative of the lung pressure of the patient(e.g. measured airway pressure), volumes indicative of the effectivelung volume of the patient (e.g. measured tidal volume), gasconcentration in expiration gases exhaled by the patient (e.g. expiredCO2), blood oxygenation (e.g. peripheral oxygen saturation, SpO2), and astress index parameter determined from a pressure-volume (P-V)relationship.

In the following, the PEEP titration phase will be described in thecontext of an exemplary embodiment in which the optimal PEEP of thepatient is determined by assessing the dynamic compliance, Cdyn, of thepatient's lungs during a stepwise decrease in PEEP. The optimal PEEPmay, in this scenario, be determined by finding a closing PEEPcorresponding to a PEEP level where alveoli starts to collapse, i.e. aclosing PEEP substantially corresponding to the alveolar closingpressure of the patient 2. The optimal PEEP of the patient may then beset by the breathing apparatus 2 to a value that is slightly higher thanthe determined closing PEEP. Preferably, the optimal PEEP is set in therange of 1-3 cmH2O above closing PEEP, and most preferably toapproximately 2 cmH2O above closing PEEP.

Closing PEEP can be determined since Cdyn is expected to change in apredictable way as PEEP is reduced during the PEEP titration phase. Amore or less distinct peak in Cdyn is expected just prior to the pointin time when alveoli start to cyclically collapse. To avoid high tidalvolumes as compliance increases, and to obtain comparable Cdyn valuesduring PEEP titration, the PEEP titration phase is performed in VCventilation mode. The tidal volume of the VC ventilation is adapted tothe relevant patient category and may, for example, be selected by thebreathing apparatus 2 based on a predicted bodyweight of the patient 3,e.g. as input to the breathing apparatus 2 by the breathing apparatusoperator. As illustrated in upper right corner of FIG. 4, the FRMplanning view may comprise an indication of the predicted bodyweight(PBW) of the patient. In the illustrated example, the tidal volume ofthe VC ventilation may be adjusted by the operator via a setting(VT/PBW) in the FRM planning view 33. The set tidal volume may beexpressed in terms of volume of breathing gas per kilo bodyweight,and/or in terms of a total volume of breathing gas per breath. Cdyn maythen, for example, be calculated by the breathing apparatus 2 based on achange in airway pressure resulting from delivery of a well-definedtidal volume of breathing gas to the lungs of the patient 3.Consequently, the breathing apparatus 2 may be configured to calculateCdyn for any given breath during PEEP titration based on set or measuredtidal volume and pressure measurements indicative of actual PEEP and PIPobtained by the one or more pressure sensors 25, 25′, 25″ of thebreathing apparatus (see FIG. 1).

The PEEP titration phase starts by first reducing the PEEP level to thePEEP titration start level and then switch from PC to VC ventilationwith RR and I:E settings corresponding to ventilation settings usedprior to initiation of FRM. The patient 3 is ventilated on each PEEPlevel for a number of breaths, and a Cdyn value is determined for eachbreath. The number of breaths on each PEEP level is set by the FRMsetting Breaths/step in the FRM planning view 33 and may, for instance,be in the range of 6-15 breaths. When the set number of breaths for agiven PEEP step has been delivered to the patient 3, the breathingapparatus 2 reduces PEEP to the next PEEP titration level. In theillustrated example, the size of each PEEP step in the PEEP titrationphase is preset to a maximum of 2 cmH2O. If the set PEEP start level islow, the size of each PEEP step may be automatically reduced by thebreathing apparatus 2. In other embodiments, the size of each PEEP stepin the PEEP titration phase may be set by the operator via auser-adjustable setting in the FRM planning view. The size of each PEEPstep in the PEEP titration phase should preferably be in the range of1-3 cmH20, and most preferably around 2 cmH2O.

The decremental decrease in PEEP during the PEEP titration phase iscontinued until a maximum Cdyn can be identified, until a set minimumPEEP level is reached, or until a predefined abortion criterion is met,as will be discussed in more detail below. The minimum PEEP level may bepreset or set by the operator via an adjustable setting in the FRMplanning view 33.

In order to accurately determine Cdyn, the breathing apparatus 3 may beconfigured to disregard any spontaneous breaths during the PEEPtitration phase, meaning that Cdyn may be calculated only for fullycontrolled breaths during the PEEP titration phase.

If PEEP titration is performed in VC mode, as in the illustratedexemplary embodiment, the PIP of the patient is not directly controlledbut a consequence of the combination of set tidal volume and complianceIn this case, it is important to adequately handle potentially high PIPduring the first PEEP levels of the PEEP titration phase, where thelungs of the patient 3 can be expected to be over distended with arelatively low compliance.

Therefore, as a first lung protective strategy should measured airwaypressure exceed the maximum PIP limit (PIP max) during a breath of PEEPtitration phase, the breathing apparatus 2 may be configured to cycleoff the breath, whereby the volume of breathing gas delivered during thebreath will not reach the set tidal volume. As long as a safety valve ofthe breathing circuit is not opened in this situation (e.g. due topatient coughing or external manipulation), the PEEP titration phase maycontinue as planned after the prematurely cycled off breath. If theairway pressure of the patient 3 reaches the maximum PIP limit for twobreaths at the same PEEP step of the PEEP titration staircase, i.e. iftwo breaths on the same PEEP step are prematurely cycled off, thebreathing apparatus 2 may be configured to immediately (typically within1-2 breaths) reduce PEEP to the next PEEP level. Cdyn values forprematurely cycled off breaths are not reliable and are not used by thebreathing apparatus 2 in the determination of the alveolar closingpressure of the patient 3.

In some situations, in particular during the first steps of PEEPtitration in VC mode, PIP may be high enough to have potentialdetrimental effect on the patient's lungs due to over distension of thelung tissue, yet not high enough to reach the maximum PIP limit.Therefore, as a second lung protective strategy, the breathing apparatus2 may be configured to monitor PIP during PEEP titration and if the PIPexceeds a secondary PIP limit being lower than the maximum PIP limit fortwo consecutive breaths, the breathing apparatus may be configured toskip any remaining breaths on the current PEEP step and reduce PEEP tothe next PEEP level. The secondary PIP limit thus serves as a maximumPIP limit for consecutive breaths at the respective PEEP step of thePEEP titration phase, For instance, the secondary PIP limit may be 35cmH2O for a “normal” patient. For obese patients, the secondary PIPlimit may be 40-45 cmH2O.

As an alternative lung protective strategy, the breathing apparatus 2may be configured to immediately reduce PEEP to the next lower PEEPlevel in response to detection of an airway pressure above the maximumPIP limit if, and only if, no previous PEEP titration step has beensuccessfully completed (i.e. if all previous PEEP steps have beenpre-maturely aborted due to the maximum PIP limit being exceeded). If,on the other hand, one or more previous PEEP steps have beensuccessfully completed, the breathing apparatus 2 may be configured toapply some of the above mentioned lung-protective strategies forconsecutive and/or non-consecutive breaths on the same PEEP step.

It should be appreciated that there are other parameters than airwaypressure that may be monitored during the PEEP titration phase to avoidpotentially harmful levels of ventilation of the patient, and that theabove mentioned lung protective strategies may be used for any monitoredparameter indicative of a potentially harmful level of ventilation ofthe patient during PEEP titration in any mode of ventilation.

Consequently, the breathing apparatus 2 may be configured toautomatically decrease PEEP to a lower, and typically the next lowerPEEP level, in response to a crossing of a threshold value of amonitored parameter indicative of a potentially harmful level ofventilation of the patient 3 during the PEEP titration phase. Thebreathing apparatus 2 may be configured to decrease PEEP to the nextPEEP level the first time the monitored parameter reaches the thresholdvalue. In other embodiments, breathing apparatus 2 may be configured notto reduce the PEEP level when the monitored parameter reaches thethreshold value for a first time, but when the monitored parameterreaches the threshold value for at least a second time at the same PEEPlevel. This has the effect of avoiding too early and uncalled-forabortion of PEEP titration on a certain PEEP level. As described above,there may be a first threshold value for any two breaths at the samePEEP level, and a second and different threshold value for two or moreconsecutive breaths at the same PEEP level. The effect of using adifferent threshold value for consecutive and non-consecutive breaths isthat premature abortion of PEEP titration on a certain PEEP level can beavoided while still effectively protecting the lungs of the ventilatedpatient 3. As also described above, the breathing apparatus 2 may beconfigured to reduce PEEP to a lower PEEP level when the monitoredparameter reaches the threshold value for a first time on a current PEEPlevel only if the threshold value has been reached on at least oneprevious (higher) PEEP level. If the threshold value has not beenreached on any of the previous PEEP levels, the breathing apparatus 2may be configured not to reduce the PEEP level when the monitoredparameter reaches the threshold value for a first time on a current PEEPstep, but to reduce PEEP when the monitored parameter reaches thethreshold value for at least a second time at the current PEEP level.This has the effect of preventing PEEP from being reduced due tooccasional events, such as patient coughing, while ensuring that PEEP isreduced when the patient seems to be ventilated on a potentially harmfullevel of ventilation.

A third lung protective strategy may also be put in place in order toavoid volutrauma due to stacked breaths in VC mode during PEEPtitration. To this end, during the PEEP titration phase, the breathingapparatus 2 may be configured not to deliver a breath normally deliveredto the patient 3 in VC mode in response to a detected breathing effortby the patient. The functionality of non-delivery of breaths in responseto patient efforts during the PEEP titration phase may be implementedeither by actively interrupting the delivery of breaths by the breathingapparatus, or by adjusting a trigger sensitivity of the breathingapparatus 3 during the PEEP titration phase. For example, a triggerlevel for measured airway pressure may be set to a very low sensitivitylevel, such as −20 cmH2O, during PEEP titration in order to avoidtriggering of breaths.

The breathing apparatus 2 may use different search algorithms foridentifying the alveolar closing pressure of the patient 2 during thePEEP titration phase. In an exemplary embodiment, the search algorithmmay be adapted to find the alveolar closing pressure of the patient byidentifying a closing PEEP at which the Cdyn parameter assumes a maximumvalue during the PEEP titration phase. This may be achieved by fittingthe Cdyn values determined for the respective PEEP steps to apolynomial. The search algorithm should be robust against noise, e.g.due to occasional spontaneous patient activity or external manipulationof the patient. To this end, the algorithm may employ statisticalmethods for disregarding “non-normal” breaths on each PEEP step, as wellas for handling too large deviations in calculated Cdyn values.

For each breath at any given PEEP step, a Cdyn value is calculated andan actual PEEP is measured. The Cdyn values and the measured PEEP valuesof all breaths at the PEEP step are collected and stored in sortedlists. When Cdyn and PEEP values for the last breath of the PEEP stephave been collected, the breathing apparatus 2 is configured to identifya sequence of breaths among the breaths of the PEEP step that has theleast standard deviation in Cdyn. The breathing apparatus 2 thencalculates representative values of Cdyn and PEEP for the PEEP step asthe mean values of Cdyn and PEEP for the identified sequence of breaths.

The representative values of Cdyn and PEEP, as well as the Cdyn standarddeviation for all PEEP steps are added to a data array that is fitted toa third or higher degree polynomial to determine any local maximum ofCdyn as a function of PEEP. If and when the local maximum has beendetermined, a check is made as to whether the determined Cdyn maximumlies within the PEEP range covered so far in the PEEP titration phase.If the Cdyn maximum lies within the PEEP titration range covered so far,the PEEP titration phase is aborted and the FRM manoeuvre continues tothe re-recruitment phase. By skipping any remaining PEEP steps of theplanned PEEP titration phase when a local maximum of Cdyn has beenidentified, the duration of the FRM manoeuvre and any discomfort to thepatient can be minimised. If the determined Cdyn maximum does not liewithin the PEEP titration range covered so far, the PEEP titration phaseis continued until a local Cdyn maximum lying within the PEEP titrationrange covered so far has been identified. If no Cdyn maximum can befound, the PEEP titration phase continues until the minimum PEEP levelhas been reached, or until a predefined abortion criterion is met.

The PEEP value for maximum Cdyn is assumed to correspond to the alveolarclosing pressure of the patient and is hence the PEEP value hereinreferred to as closing PEEP.

In some situations, the breathing apparatus 2 will be unable todetermine a reliable maximum Cdyn and hence unable to reliably determinea closing PEEP corresponding to the alveolar closing pressure of thepatient. The breathing apparatus may for instance be unable to identifya maximum Cdyn during the PEEP titration phase due to any of, or anycombination of, the following reasons:

-   -   Noisy Cdyn measurements, e.g. due to too high degree of        spontaneous breathing activity by the patient, secretions in an        endotracheal tube or the patient circuit of the ventilation        system, or external manipulation of the patient;    -   Constantly falling Cdyn, e.g. due to too low recruitment        pressure or too low start level for PEEP titration, or due to        the fact that the optimal PEEP is the start level for PEEP        titration;    -   Constantly rising Cdyn, e.g. due to PEEP-independent lungs, i.e.        healthy lungs without need for recruitment, or due to high        leakage during expiration;    -   Substantially constant Cdyn, i.e. very small variations in Cdyn        during PEEP titration, e.g. due to highly heterogeneous        (“non-recruitable”) lungs.

The breathing apparatus 2 may be configured to handle all thesesituations in a similar manner, with only minor differences in theinformation communicated to the operator.

Whenever a maximum Cdyn cannot be identified during PEEP titration, thebreathing apparatus 2 is configured to abort the FRM manoeuvre and toreset ventilation settings, including alarm limits, to the settings usedprior to the FRM manoeuvre. The breathing apparatus 2 may further beconfigured to present information on why a maximum Cdyn could not besuccessfully identified, including at least one possible root cause tothe unsuccessful identification.

The breathing apparatus 2 may further be configured to automaticallyabort the FRM manoeuvre as soon as it can be established that a closingPEEP cannot be reliably determined. This is advantageous in that thepatient is relieved from the discomfort and potential risks associatedwith the FRM manoeuver as soon as it can be established that themanoeuver will not be successful. The breathing apparatus 2 may, forinstance, be configured to abort the FRM manoeuver if at least onepredefined abortion criterion for the PEEP titration phase is met. Theat least one abortion criterion may comprise a criterion for Cdyn.Preferably, the at least one abortion criterion comprises a criterionfor a Cdyn trend established during the PEEP titration phase. Forexample, the breathing apparatus 2 may be configured to abort the FRMmanoeuvre in case a Cdyn trend indicates that no reliable Cdyn maximumis likely to be identified by the breathing apparatus. For instance, ifthe Cdyn trend indicates a constantly raising Cdyn, a constantly fallingCdyn, or a substantially constant Cdyn, the breathing apparatus mayabort the FRM manoeuvre.

If the at least one abortion criterion is met, the breathing apparatus 2is configured to abort the FRM manoeuvre and return to the ventilationmode and ventilation settings used prior to initiation of the FRMmanoeuvre.

Consequently, Cdyn may be monitored and used by the breathing apparatus2 not only to determine the optimal PEEP but also to establish a trendthat can be used to predict whether or not the optimal PEEP can bereliably determined later on during the PEEP titration phase. Theability of the breathing apparatus to predict whether it will bepossible to reliably determine an optimal PEEP of the patient later onduring the PEEP titration phase, and to abort the FRM manoeuvre if not,is advantageous in that an unsuccessful FRM manoeuvre can be aborted ata very early stage.

Examples of other parameters that may be monitored and used to establisha parameter trend that is indicative on whether or not it will bepossible to reliably determine closing PEEP later on during thetitration phase is a phase II slope parameter derived from a volumetriccapnogram (Vcap), and a stress index derived from a pressure-volume(P-V) relationship. Consequently, the breathing apparatus 2 may use theVcap phase II slope and/or the stress index to predict whether or notthe optimal PEEP can be reliably determined later on during the PEEPtitration phase

As well known in the art, measurements of expired CO2 and volume can beused to establish a volumetric capnogram, where expired CO2 is plottedagainst exhaled volume. This allows for breath-to-breath quantificationof alveoli that are ventilated but not perfused and measurement ofalveolar dead space. The volumetric capnogram of each breath comprisesthree phases, where the second phase (phase II) represents gas comingfrom regions that are in the transition between anatomic and alveolargas compartments. This includes gas emptying from small airways andalveoli that are close to the main airways. During this phase there isan almost linear increase in CO2. A reduction in PEEP will cause theslope of this substantially linear increase in CO2 (phase II slope) toincrease until a point in time where alveoli start to collapse,whereafter a further reduction in PEEP will cause the slope to decrease.Consequently, during the PEEP titration phase, the Vcap phase II slopewill assume a maximum value at or close to the alveolar dosing pressureof the patient. Therefore, the breathing apparatus 2 may be configuredto monitor the phase II slope of a volumetric capnogram of the patientduring PEEP titration, and to determine an optimal PEEP of the patientbased on the PEEP level for which the maximum phase slope is obtained.The PEEP value for the maximum phase II slope correspond to the dosingPEEP.

Furthermore, the breathing apparatus 2 may be configured to establish atrend curve for the phase II slope of the volumetric capnogram coveringmultiple PEEP steps. Such a trend curve may resemble the phase II trendcurve illustrated in FIG. 8 in EP1579882A1. This trend curve may beanalysed by the breathing apparatus 2 in the same way the Cdyn trendcurve is analysed in the example described above. If, for instance, thephase II slope curve is substantially constant, constantly raising orconstantly falling, it can be assumed that it will not be possible toreliably determine a maximum for the phase II slope and thus notpossible to reliably determine an optimal PEEP of the patient during thePEEP titration phase. In this case, the breathing apparatus 2 may abortthe FRM manoeuvre. The breathing apparatus 2 may be configured todetermine the phase II slope on a breath-by-breath basis during PEEPtitration, and to process the phase H slope measurements the way theCdyn measurements are processed in the example described above, e.g. interms of averaging for each PEEP step, etc.

Stress index is a parameter that is indicative of the pulmonary stressof a ventilated patient, which parameter may be determined byestablishing a P-V relationship for a single breath and determining theprofile (i.e. the concavity or convexity) of the P-V relationship. Theprofile is straight (stress index=1) when no stress is present, convex(stress index<1) when there is a risk for overdistension, and concave(stress index>1) when alveoli are opened up during the breath. Moreinformation about the stress index parameter and how to use the stressindex in the assessment of pulmonary stress can be found in e.g. U.S.Pat. No. 6,715,975B2. Typically, at the start of PEEP titration, thelungs of the patient will be partly overdistended, resulting in a stressindex>1. However, as PEEP approaches an optimum PEEP for the patient,the stress index will approach one. Consequently, the breathingapparatus 2 may be configured to monitor the stress index of the patientduring the PEEP titration phase, and to determine an optimal PEEP of thepatient based on the PEEP value for which the monitored stress indexassumes a value of one.

Furthermore, the breathing apparatus 2 may be configured to establish atrend curve for the stress index covering multiple PEEP steps. Such atrend curve should approach one if the optimal PEEP of the patient islikely to be found during the PEEP titration phase. If the stress indextrend curve does not approach one (e.g. if the stress index trend curveis substantially constant or even diverging from stress index=1), thebreathing apparatus 2 can predict that it will not be possible toreliably determine an optimal PEEP of the patient during the PEEPtitration phase, whereby the breathing apparatus 2 may abort the FRMmanoeuvre. The breathing apparatus 2 may be configured to determine thestress index on a breath-by-breath basis during PEEP titration, and toprocess the stress index measurements the way the Cdyn measurements areprocessed in the example described above, e.g. in terms of averaging foreach PEEP step, etc.

Above, it has been described that the breathing apparatus may beconfigured to predict if it will be possible to reliably determine anoptimal PEEP later on during the PEEP titration phase based on a trendof a monitored parameter (e.g. Cdyn, Vcap phase II slope or stressindex), and to abort the FRM manoeuvre if reliable determination ofoptimal PEEP will not be possible. It should be noted that the breathingapparatus may also be configured to abort the FRM manoeuvre if thequality of at least one measurement signal required for determination ofthe monitored parameter is poor. The breathing apparatus 2 may beconfigured to assess the signal quality and to predict whether or not itwill be possible to reliably determine the optimal PEEP of the patientgiven the quality of the at least one measurement signal. If, based onthe quality of the at least one measurement signal, it is predicted thatan optimal PEEP cannot be reliably determined, the breathing apparatus 2may abort the FRM manoeuvre.

FIG. 5 illustrates an exemplary FRM workflow view 35 of the OLTinterface. When the operator is done planning the FRM manoeuvre in theFRM planning view 33 of FIG. 4 and chooses to confirm the FRM settings,e.g. by pressing a continue button displayed in the FRM planning view,the breathing apparatus 3 displays the FRM workflow view 35 of FIG. 5,through which the operator may initiate and monitor the FRM manoeuvre.

The exemplary FRM workflow view 35 in FIG. 5 comprises a pressuredisplay field 36 illustrating the planned pressure trajectories A and Bfor PIP and PEEP. As the FRM manoeuvre progresses, the planned PIP andPEEP trajectories A and B are replaced by curves A′ and B′ representingmeasured PIP and PEEP. The pressure display field 36 comprises aposition indicator 37 indicating in real time a current position alongany or both of the pressure trajectories for PIP and PEEP. The pressuredisplay field 36 further comprises a closing PEEP indicator 39indicating the value and positon of the closing PEEP determined duringPEEP titration. The pressure display field 36 further comprise a PIPlimit indicator 41 indicating the maximum PIP limit set in the FRMplanning view 33. Yet further, the pressure display field 36 comprisescurrent values of PIP, Pdrive and PEEP.

The exemplary FRM workflow view 35 further comprises a Cdyn displayfield 43. The Cdyn display field comprises a Cdyn curve C representingCdyn values determined for the breaths of the FRM manoeuvre. The Cdyndisplay field 43 further comprises a maximum Cdyn indicator 45indicating the value and position of the maximum Cdyn determined duringPEEP titration. In the illustrated embodiment, the breathing apparatus 3is devise with a CO2 module for measuring CO2 in expiration gasesexhaled by the patient 3, and the Cdyn display field 43 furthercomprises a CO2 elimination curve D representing the tidal volume of CO2elimination (VTCO2) during the breaths of the FRM manoeuvre. The Cdyndisplay field 43 further comprises current values of Cdyn and VTCO2. Incases where other parameters than Cdyn are used to determine the optimalPEEP of the patient, such as the above mentioned phase II slopeparameter or stress index parameter, trend curves and/or current valuesfor these parameters may be displayed instead of, or in addition to, theCdyn curve C and the current value of Cdyn.

The FRM workflow view 35 further comprises a volume display field 47.The volume display field 35 comprises an inspiratory volume curve Erepresenting the inspiratory tidal volume, VTi, during breaths of theFRM manoeuvre. The tidal volume display field 47 further comprises atidal volume indicator 49 indicating the inspiratory tidal volume of thepatient 3 at closing PEEP. Information on tidal volume at closing PEEPis somewhat redundant in the illustrated embodiment where PEEP titrationis performed in VC mode using constant tidal volume, but is highlyrelevant in other conceivable embodiments in which PEEP titration isperformed in PC mode. The volume display field 47 further comprises anexpiratory volume curve F representing the expiratory tidal volume, VTe,of breaths of the FRM manoeuvre. The volume display field 47 furthercomprises current values of VTi and VTe.

The above mentioned curves A′, B′, C-F of the FRM workflow view 35 thusconstitute real time plots of breath-to-breath trend curves for theparameters PIP, PEEP, Cdyn, VTCO2, VTi and VTe.

The FRM workflow view 35 further comprises a flow display field 51. Theflow display field comprises a flow curve G representing respiratoryflow during the most recent breath or breaths. The exemplary flow curveG is a real time plot of airway flow. In some embodiments (not shown),the FRM workflow view 35 may comprise at least one interactive element,such as one or more buttons, allowing the operator to toggle betweenreal time plots of measured flow, pressure, trans-pulmonary pressure,and/or Edi signals, possibly in combination with numeric presentation ofadditional parameters.

In the illustrated exemplary embodiment, Cdyn max (70,1) was found for aclosing PEEP of 11 cmH2O during the PEEP titration phase.

FRM: Re-Recruitment

The re-recruitment phase of the FRM manoeuvre is a shorter version ofthe recruitment phase. The purpose of the re-recruitment phase is tore-open any alveoli that have collapsed during the PEEP-titration phase,and in particular during ventilation at the lowest steps of the PEEPtitration staircase.

In the illustrated embodiment, when going from the PEEP titration phaseto the re-recruitment phase, the breathing apparatus 2 changesventilation mode from the VC mode of the PEEP titration phase to PCmode. Like in the recruitment phase, the PEEP and PIP are incrementallyincreased up to maximum PEEP and PIP values to gradually prepare thelungs of the patient for high pressure ventilation. The maximum PIP ismaintained for a number of breaths to ensure that any alveoli that havecollapsed during the PEEP titration phase are re-opened during there-recruitment phase.

To serve the purpose of re-opening any closed alveoli, the maximum PIPat the plateau of the re-recruitment staircase should be higher than thealveolar opening pressure of the patient 3. If the breathing apparatus 2is devised and configured to determine the alveolar opening pressure ofthe patient 3 during the recruitment phase, e.g. from expiratory CO2measurements as explained above, the maximum PIP of the re-recruitmentphase may be automatically set to a value that is slightly higher thanthe alveolar opening pressure. This means that the maximum PIP of there-recruitment phase may be set to a lower value than the maximum PIP ofthe recruitment phase, thereby reducing the adverse effects of highpressure ventilation. In another exemplary embodiment, there-recruitment phase may be carried out with the same settings as therecruitment phase but with a reduced number of breaths per PEEP step(e.g. half the number), and with a reduced number of breaths at themaximum PEEP (and maximum PIP) plateau (e.g. half the number). In theillustrated embodiment, this means that the recruitment parameters PEEPmax, PIP max, PEEP incr/step and Recruitment rate in the FRM planningview shown in FIG. 4 can be used also for the re-recruitment phase,whereas the number of breaths per PEEP step and the number of breaths atmaximum PEEP may be set to e.g. half the values of the respectiverecruitment parameters Breaths/step and Breaths at PEEP max, round-up tothe nearest integer.

FRM: Post-RM

After the re-recruitment phase of the FRM manoeuvre, the breathingapparatus 2 enters the post-RM phase and starts ventilating the patientwith optimised ventilation settings determined during the FRM manoeuvre.The optimised ventilation settings comprises at least the optimal PEEPdetermined during PEEP titration.

Furthermore, if post-RM ventilation is carried out in PC mode, thebreathing apparatus enters the post-RM phase with a post-RM drivingpressure that is optimised to the changed lung dynamics of the patient3. This optimised post-RM driving pressure is hereinafter referred to asthe optimal driving pressure (optimal Pdrive). The optimal drivingpressure may be automatically determined by the breathing apparatus 2based on measured PEEP and Cdyn values during the PEEP titration phase.In one exemplary embodiment, the breathing apparatus 2 is configured todetermine an optimal driving pressure for post-RM ventilation which,given the optimal PEEP and a PEEP-Cdyn relationship established duringthe PEEP titration phase, results in a tidal volume corresponding to thetidal volume set for the PEEP titration phase. The optimal drivingpressure may, for instance, be set to VT_(desired)/C_(dyn_opt), whereVT_(desired) is a desired tidal volume for the post-RM phase, e.g.corresponding to the tidal volume set for the PEEP titration phase (viathe VT/PBW setting in the planning view 33), and C_(dyn_opt) is the Cdynvalue corresponding to the optimal PEEP.

If post-RM ventilation is carried out in VC mode, the breathingapparatus enters the post-RM phase with a tidal volume corresponding tothe tidal volume set for the PEEP titration phase. Alternatively, thetidal volume of post-RM VC ventilation may be automatically set tocorrespond to a tidal volume set for a period of baseline ventilationpreceding the FRM manoeuvre, i.e. to a tidal volume set for pre-RM VCventilation.

When entering into the post-RM phase, the breathing apparatusautomatically switches ventilation mode to a predefined ventilation modethat is either automatically determined by the breathing apparatus 2 orpreset by the breathing apparatus operator, e.g. in the FRM planningview of the OLT tool. All post-RM ventilation settings except for PEEPand driving pressure (in PC mode) or tidal volume (in VC mode) may beinitiated from corresponding settings of the baseline ventilationpreceding the FRM manoeuvre.

Preferably, the breathing apparatus 2 is configured to automaticallyswitch to a previous ventilation mode used during baseline ventilationpreceding the FRM manoeuvre, and to enter the post-RM phase in theprevious ventilation mode but with optimised ventilation settings, asdescribed above. That the breathing apparatus 2 is configured toautomatically return to the ventilation mode that was used prior to theFRM manoeuvre is advantageous in that manual workload is minimised andin that the breathing apparatus operator does not have to remember theventilation mode or ventilation settings used prior to the FRMmanoeuvre.

The post-RM phase is an evaluation phase in which the patient 3 isventilated at the optimal PEEP for a few breaths (typically around fivebreaths) during which post-RM comparison data to be compared with thepre-RM comparison data obtained during the pre-RM phase is collected. Asmentioned above, the comparison data may e.g. comprise data on Pdrive,Cdyn, PEEP, PIP and VTi.

Following the post-RM collection of comparison data, the breathingapparatus 2 is configured to present, to the breathing apparatusoperator, evaluation data indicative of the effect of the FRM manoeuvreon the patient 3. The evaluation data comprises or is derived from thecomparison data collected during the pre-RM phase (pre-RM comparisondata) and the comparison data collected during the post-RM phase(post-RM comparison data). The evaluation data may comprise numericalvalues and/or a graphical representation of the pre- and post-RMcomparison data. Preferably, the evaluation data comprises numericalvalues and/or graphical representations of at least pre- and post-RMPdrive and Cdyn values. For instance, the evaluation data may comprise acomparison table including numerical values for one or more of Pdrive,Cdyn, and VTi for both the pre-RM phase and the post-RM phase. Insteadof, or in addition to, numerical values of pre-RM and post-RM comparisondata, the evaluation data may comprise symbols indicating whether theparameters of the comparison data, e.g., Pdrive, Cdyn, and VTti, haveimproved or not improved as a result of the FRM manoeuvre. For example,the parameters may be displayed in association with graphics, such as arespective symbol or graph, indicating whether the respective parametershave improved or not improved as a result of the FRM. It should beappreciated that the pre- and post-RM comparison data, and thus theevaluation data presented to the operator, may comprise other keyrespiratory parameters than those mentioned above.

FIG. 6 illustrates an exemplary embodiment in which the evaluation datais displayed in a comparison table 53 of the RM workflow view 35 of theOLT interface. In this exemplary embodiment, the evaluation datacomprise numerical values for pre- and post-RM Pdrive, Cdyn and VTi, aswell as symbols 55 indicating whether or not there has been anyimprovement in Cdyn or Pdrive as a result of FRM. Each symbol may beprovided with a colour indicating either an improvement (e.g. greencolour), no substantial change (e.g. white colour), or a deterioration(e.g. orange colour) in the associated parameter.

After the post-RM collection of comparison data, the breathing apparatus2 is further configured to present, to the breathing apparatus operator,suggestions on optimised ventilation settings for the new baselineventilation following the FRM manoeuvre, which ventilation settings arebased on one or more parameters determined during the PEEP titrationphase. The suggested ventilation settings comprises at least a suggestedPEEP for new baseline ventilation, which suggested PEEP may correspondto the optimal PEEP set for the post-RM phase. The suggested ventilationsettings may further comprise a suggested driving pressure for newbaseline ventilation in PC mode, which suggested driving pressurecorresponds to the optimal driving pressure used during the post-RMphase (if performed in PC mode). The suggested ventilation settings mayfurther comprise a suggested tidal volume for new baseline ventilationin VC mode, which suggested tidal volume corresponds to the tidal volumeused during the post-RM phase (if performed in VC mode).

The suggested ventilation settings may be displayed in association withthe evaluation data, thereby indicating to the operator the ventilationsettings for which the post-RM comparison data were obtained. Forexample, the breathing apparatus 2 may be configured to display thesuggested ventilation settings in association with the comparison table53. The breathing apparatus 2 may further be configured to prompt theoperator to accept the suggested ventilation settings for new baselineventilation, e.g. by causing an accept button to be displayed inrelation to the suggested ventilation settings. In this way, theoperator can easily compare the pre-RM comparison data with the post-RMcomparison data and chose to accept the suggested ventilation settingsonly if ventilation with the suggested ventilation settings (i.e.post-RM ventilation) has shown a positive effect on the ventilatedpatient. That ventilation with the suggested ventilation settings showsa positive effect on the ventilated patient indicates that the suggestedventilation settings are better tailored to the changed lung dynamics ofthe patient than the pre-RM ventilation settings. Furthermore, assumingthat the pre-RM ventilation settings were properly adjusted, itindicates that the FRM manoeuvre was successful and that alveoli havebeen successfully recruited.

If the operator chooses to accept the suggested ventilation settings,the breathing apparatus 2 continues to ventilate the patient 3 using thesuggested ventilation settings used during the post-PM phase. No changesin ventilation mode or ventilation settings are made. Consequently, bysimply accepting the optimised ventilation settings suggested by thebreathing apparatus 2, the patient will automatically be ventilatedusing the same ventilation mode after the FRM manoeuvre as before theFRM manoeuvre, with optimised ventilation settings adapted to changes inlung dynamics caused by the FRM manoeuvre.

If, on the other hand, the operator chooses not to accept the suggestedventilation settings, or does not actively choose to accept thesuggested ventilation settings for a predetermined acceptance time ofe.g. 1-5 minutes, the breathing apparatus may be configured to revert toall or some of the pre-RM ventilation settings, including pre-RMventilation settings for PEEP and driving pressure (in PC mode) andtidal volume (in VC mode). Consequently, the breathing apparatus 2 maybe configured to automatically revert to settings that may be regardedas “safe settings” should the breathing apparatus operator not acceptthe suggested ventilation settings within a predetermined acceptancetime. This feature has the effect of improving patient safety as thereis always a risk that ventilation settings that are initiated withoutinvolvement of a clinician are not suited for long-term ventilation ofthe patient. There may, for instance, be situations where ventilationsettings should be optimised with regard to other parameters than thedynamic compliance of the patient.

Of course, the breathing apparatus 2 may also be configured to presentthe suggested ventilation settings with possibilities for the operatorto modify the settings before accepting them, i.e. in form ofuser-adjustable ventilation settings. Thus, the finally selectedventilation settings for new baseline ventilation following the FRMmanoeuvre may deviate from the suggested ventilation settings.

When the operator has accepted or denied the suggested ventilationsettings, or when the predetermined acceptance time has lapsed, the FRMmanoeuvre is ended and the breathing apparatus 2 displays the view thatwas displayed on the display 32 of the breathing apparatus prior toentering the FRM planning view 33 of the OLT tool.

Before ending the FRM manoeuvre, however, the breathing apparatus 2 isconfigured to save and store an FRM recording comprising characteristicsof the FRM manoeuvre in the memory 31 of the computer 15. Thecharacteristics of the FRM recording comprises the FRM settings set inthe FRM planning view 33, the evaluation data comprising the pre-RM andpost-RM comparison data, and the suggested and finally selectedventilation settings for new baseline ventilation following the FRMmanoeuvre. The FRM recording also comprises the breath-by-breath trenddata from which the curves A′, B′, C-F in the workflow view 35 weregenerated in real time during the FRM manoeuvre, i.e. breath-by-breathtrend data for the parameters PIP, Pdrive, PEEP, Cdyn, VTCO2, VTi andVTe.

The characteristics of the recordings of historical FRM manoeuvres canbe studied by the operator via an FRM trend view (not shown) of the OLTtool, or exported to another software application for subsequentanalysis. The breath-by-breath trend data of the recordings enables thebreathing apparatus 2 to present any of, or any combination of, thebreath-by-breath trend curves A′, B′, C-F from previous FRM manoeuvresto the operator, in order for the operator to study the curve(s)retrospectively. Such a breath-by-breath trend curve from a previous FRMmanoeuvre is hereinafter referred to as a trend curve recording. Thebreathing apparatus 2 may be configured to display trend curverecordings for one or more of the parameters PIP, Pdrive, PEEP, Cdyn,VTCO2, VTi and VTe in the FRM trend view. The breathing apparatus 2 mayfurther be configured to display, in association with the one or moretrend curve recordings, any of, or any combination of, the FRM settingsof the recorded FRM manoeuvre, the evaluation data of the recorded FRMmanoeuvre, and the suggested and finally selected ventilation settingsfor new baseline ventilation following the recorded FRM manoeuvre. If nomaximum Cdyn was found during PEEP titration, information (e.g. the rootcause) on why Cdyn was not found may also be displayed.

Before ending the FRM manoeuvre, the breathing apparatus 2 may furtherbe configured to automatically adjust relevant alarm limits. Some alarmlimits may be reset to the limits used prior to the FRM manoeuvre whileother alarm limits may, if the breathing apparatus operator has acceptedthe suggested ventilation settings, be set based on the suggestedventilation settings for new baseline ventilation following the FRMmanoeuvre. Consequently, the breathing apparatus 2 may be configured toautomatically adjust alarm limits for relevant respiratory parametersbased on the suggested ventilation settings. For example, the breathingapparatus 2 may be configured to automatically adjust the alarm limitsfor maximum PIP, maximum PEEP, and/or a minimum PEEP, based on thesuggested ventilation settings. The alarm limit for maximum and/orminimum PEEP may be adjusted based on the optimal PEEP suggested for newbaseline ventilation following the FRM manoeuvre. The alarm limit formaximum PIP may be adjusted based on the optimal PEEP and the optimaldriving pressure suggested for the new baseline ventilation followingthe FRM manoeuvre. This driving pressure may be any of a drivingpressure used prior to the FRM manoeuvre (if no changes in Pdrive aresuggested) or a new driving pressure suggested for the new baselineventilation following the FRM manoeuvre. The feature of automaticallyupdating the alarm limits is advantageous in that in minimises manualworkload and improves patient safety since the breathing apparatusoperator does not have remember to update the alarm limits to suit thechanged lung dynamics of the patient 3 following the FRM manoeuvre.

The breathing apparatus 2 may further be configured to display the newalarm limits to the operator, and, optionally, to prompt the operator toaccept the new alarm limits before they are put into use. Of course, thenew alarm limit settings may be user-adjustable in order for theoperator to adjust the settings before accepting them for use.

The Quick Recruitment Manoeuvre—QRM

The exemplary QRM manoeuvre illustrated in FIG. 3 will now be describedin more detail with reference to FIGS. 7 and 8. The QRM manoeuvre andthe procedure for carrying out an QRM manoeuvre may include thefollowing phases:

-   -   1) A planning phase for planning the QRM manoeuvre by selecting        recruitment and post-RM settings;    -   2) A pre-RM phase involving collection of comparison data        indicative of the situation prior to QRM;    -   3) A recruitment phase for opening up collapsed alveoli,        comprising:        -   a. a recruitment pre-conditioning phase of stepwise increase            of PEEP and PIP to prepare lung for recruitment, and        -   b. a plateau recruitment phase involving a potentially            prolonged last step of the recruitment staircase, and    -   4) A post-RM phase involving ventilation with pre-defined PEEP,        with initial collection of comparison data for comparison with        pre-RM comparison data.        QRM: Planning Phase

In general, the planning phase of the QRM manoeuvre is similar to theplanning phase of the FRM manoeuvre except for minor differences in therange of adjustable settings in the planning view of the respectivemanoeuvre. An exemplary QRM planning view 57 comprising QRM settings forconfiguring the QRM manoeuvre is illustrated in FIG. 7.

As shown in FIG. 7, the QRM planning view 57 for planning the QRMmanoeuvre is very similar to the FRM planning view 33 for planning theFRM manoeuvre, illustrated in FIG. 4. Just like the FRM planning view33, the QRM planning view 57 includes settings for maximum PEEP (PEEPmax), maximum PIP (PIP max), incremental increase in PEEP (PEEPincr/step), respiratory rate (Recruitment rate), breaths per PEEP stepduring recruitment (Breaths/step), and breaths at maximum PEEP (Breathsat PEEP max). The QRM planning view is further seen to comprise asetting for post-RM PEEP (Post-RM PEEP), which setting will be describedin more detail below.

Similar to the FRM planning view 33, the QRM planning view 57 furthercomprises a visualisation 59 of the planned pressure trajectories forthe QRM manoeuvre. In the pressure trajectory visualisation, referencesign H denotes a planned PIP trajectory and reference sign I denotes aplanned PEEP trajectory for the QRM manoeuvre.

When not preceded by a previous FRM manoeuvre, the QRM settings aredefault settings initiated for the relevant patient category. If, on theother hand, an FRM manoeuvre has previously been performed for the samepatient 3, the settings used for the previous FRM may be used asproposed settings for the QRM manoeuvre, or for multiple QRM manoeuvresfollowing an FRM manoeuvre. Preferably, also results from the previouslyperformed FRM manoeuvre, e.g. the optimal PEEP determined during thePEEP titration phase of previous FRM manoeuvre, are used to initiate thesettings for the QRM manoeuvre.

By using the settings and/or results from a previous FRM manoeuvre toinitiate suggested settings for the QRM manoeuvre, the QRM can beinitiated quickly, with a minimum of manual input of information to thebreathing apparatus.

In the illustrated embodiment, the QRM is assumed to be performed forthe same patient 3 as the FRM manoeuvre described with reference toFIGS. 4-6, at a later point in time. Some QRM settings in the QRMplanning view 57 may be initiated from the settings of the previous FRMmanoeuvre. This applies, for example, to the QRM settings PEEPincr/step, Recruitment rate, Breaths/step and Breaths at PEEP max. Itmay, in some embodiments, also apply to the QRM settings PIP max and/orPEEP max defining the maximum PIP and maximum PEEP of the recruitmentphase of the QRM manoeuvre. Other QRM settings are initiated from theresult of the FRM manoeuvre. This applies, for example, to the QRMsetting for Post-RM PEEP. It may, in some embodiments, also apply to theQRM settings PIP max and/or PEEP max.

In embodiments where the PIP max and/or PEEP max settings of the QRMmanoeuvre are initiated from results of the FRM manoeuvre, the settingsmay be initiated based on e.g. the optimal PEEP and/or the optimaldriving pressure determined during the PEEP titration phase of the FRMmanoeuvre. In embodiments where the optimal PEEP is determined based ona maximum Cdyn of the PEEP titration phase, this means that the PIP maxand/or PEEP max settings of the QRM manoeuvre are initiated from Cdynvalues obtained for different pressure levels during the PEEP titrationphase of the previous FRM manoeuvre. Instead, or in addition, the PIPmax and/or PEEP max settings may be initiated based on an alveolaropening pressure of the patient 3, as determined during the recruitmentphase of the previous FRM manoeuvre. An effect of using results from aprevious FRM manoeuvre in the initiation of the PIP max and PEEP maxsettings for the QRM manoeuvre is that the maximum pressure levels canbe set in relation to known lung dynamics of the patient. In this way,the maximum PIP level may be set to a lower level than if it was to beset to guarantee proper recruitment of alveoli without knowledge on thelung dynamics of the patient.

The setting for post-RM PEEP of the QRM manoeuvre is preferablyinitiated based on the optimal PEEP determined during the PEEP titrationphase of the previous FRM manoeuvre. Preferably, the post-RM PEEPsetting of the QRM manoeuvre is set to substantially correspond to theoptimal PEEP determined during the FRM manoeuvre. Since the pressuretrajectories for PEEP and PIP during QRM are set to resemble thepressure trajectories during the recruitment phase of the previous FRMmanoeuvre, it can be assumed that the lung dynamics of the patient willbe affected in a similar way by the QRM manoeuvre as by the FRMmanoeuvre, and thus that a post-QRM PEEP corresponding to the optimalPEEP determined during FRM will be well-adapted to the post-QRM lungdynamics of the patient.

When the QRM settings are accepted by the breathing apparatus operator,the QRM planning view 57 is closed and a QRM workflow view similar tothe FRM workflow view 35 in FIG. 4 is opened.

An exemplary QRM workflow view 59 is illustrated in FIG. 8. As mentionedabove, the QRM workflow view 59 is similar to the FRM workflow view 35,illustrated in FIG. 4, and same reference numerals in the differentviews are used to denote the same elements. The main difference betweenthe views is that, in the pressure field 36 of the QRM workflow view 59,the planned and measured PIP and PEEP trajectories H, I, H′, I′ for theQRM manoeuvre have replaced the planned and measured PIP and PEEPtrajectories A, B, A′, B′ in the FRM workflow view 35.

Once the QRM manoeuvre is initiated by the operator, e.g. by actuating abutton in the QRM workflow view 59, the breathing apparatus 2 initiatesthe QRM manoeuvre and enters the pre-RM phase of the QRM manoeuvre.

QRM: Pre-RM Phase

The pre-RM phase of the QRM manoeuvre is typically identical to thepre-RM phase of the FRM manoeuvre. In short, this means that thebreathing apparatus 2 ventilates the patient 3 for a few breaths with acurrent ventilation mode and current ventilation settings, and collectspre-RM comparison data to be compared with post-RM comparison collectedduring the post-RM phase following the recruitment phase of the QRMmanoeuvre. The breathing apparatus further changes alarm limits formaximum PEEP and maximum PIP, based on the QRM settings PEEP max and PIPmax, and pre-mutes alarms for a predetermined time period (e.g. 2minutes) to avoid minute ventilation alarms and/or CO2 alarms. If thecurrent ventilation mode is not a PC mode, the breathing apparatuschanges 2 ventilation mode to PC mode after the data collection periodof the pre-RM phase. This may, for instance, be achieved by setting adriving pressure to reach a previous tidal volume, aninspiration-to-expiration ratio I:E to 1:1, and a respiratory rate inaccordance with the Recruitment rate set in the QRM planning view 57.The breathing apparatus 2 then starts ventilating the patient 3 in PCmode at a ventilation level constituting the base level of the QRMrecruitment staircase.

In all other aspects, the pre-RM phase of the QRM manoeuvre correspondsto the pre-RM phase of the FRM manoeuvre.

QRM: Recruitment Phase

The recruitment phase of the QRM manoeuvre is similar to the recruitmentphase of the FRM manoeuvre. The breathing apparatus 2 steps through theQRM recruitment staircase based on the QRM settings of the QRM planningview 57 in the way the breathing apparatus steps through the FRMrecruitment staircase based on the FRM settings of the FRM planning view33 during the FRM manoeuvre. As mentioned above, the settings formaximum PEEP and/or maximum PIP of the QRM staircase may differ from themaximum PEEP and/or maximum PIP used for the FRM manoeuvre. In all otheraspects, the QRM recruitment staircase resembles the FRM recruitmentstaircase.

QRM: Post-RM Phase

After the recruitment phase of the QRM manoeuvre, the breathingapparatus 2 enters the post-RM phase of the QRM manoeuvre. The post-RMphase of the QRM manoeuvre is similar to the post-RM phase of the FRMmanoeuvre, except for the selection of PEEP (post-RM PEEP).

In the FRM manoeuvre, the breathing apparatus 2 may enter the post-RMphase with an optimal PEEP determined from measurements made during thePEEP titration phase. In the QRM manoeuvre, however, where there is noPEEP titration phase, the breathing apparatus 2 enters the post-RM phasewith a ventilation mode and ventilation settings corresponding to aventilation mode and ventilation settings used during baselineventilation preceding the QRM manoeuvre, except for the setting of PEEP.The post-RM PEEP is set in accordance with the Post-RM PEEP setting inthe QRM planning view 57, as described above. Consequently, thebreathing apparatus 2 typically enters the post-RM phase of the QRMmanoeuvre with a PEEP that is set based on an optimal PEEP determinedduring a PEEP titration phase of a previously performed FRM manoeuvrefor the same patient. As described above, this has the effect of settinga PEEP for the post-RM phase of the QRM manoeuvre (and typically for thenew baseline ventilation following the QRM manoeuvre) which, assumingly,is well-adapted to the post-RM lung dynamics of the ventilated patient.

In all other aspects, the post-RM phase of the QRM manoeuvre correspondsto the post-RM phase of the FRM manoeuvre, described above.

In short, this means that the breathing apparatus 2 may ventilate thepatient 3 for a few breaths using the set post-RM PEEP while collectingpost-RM comparison data; present evaluation data indicative of theeffect of the QRM manoeuvre to the breathing apparatus operator; promptthe operator to accept suggested ventilation settings based on thepresented evaluation data; save and store a recording of characteristicsof the QRM manoeuvre for subsequent post-QRM analysis; set new alarmlimits for relevant respiratory parameters, such as maximum PEEP,maximum PIP and/or minimum PEEP, based on the set post-RM PEEP; and,optionally, prompt the operator to accept the new alarm setting beforeit is put into use.

The QRM manoeuvre may also be performed without the evaluation phase,whereby the manoeuvre does not comprise collection of pre- or post-RMcomparison data, nor presentation of evaluation data to the operator. Inthis case, the operator is not prompted to acknowledge or accept thesuggested ventilation settings (comprising at least the Post-RM PEEPsetting). Instead, the breathing apparatus is configured to use thePost-RM PEEP setting during the new baseline ventilation following theQRM manoeuvre without acknowledgement from the operator.

It should be appreciated that whereas actions and method steps involvingthe supply of breathing gas to the patient 3 are typically performed bythe breathing apparatus 2 of the ventilation system 1, other actions andmethod steps of the above described FRM and QRM manoeuvres may beperformed by sub-systems or devices forming part of the ventilationsystem, such as a patient monitoring system (not shown) for monitoringthe patient 3 and the effects on the patient of the mechanicalventilation. For example, the functionality for configuring, initiating,monitoring and evaluating the FRM and QRM manoeuvres may reside in sucha patient monitoring system, or an external computer connectable to thebreathing apparatus or the patient monitoring system. Consequently, itshould be realised that the above described OLT tool may residepartially or entirely within any of the breathing apparatus 2, anexternal patient monitoring system or an external computer.

FIG. 9 illustrates a method for lung recruitment of a mechanicallyventilated patient, according to an exemplary embodiment of thedisclosure. With simultaneous reference made to previous drawings, themethod is typically a computer-implemented method that is performed bythe breathing apparatus 2 upon execution of a computer program by thecomputer 15 of the breathing apparatus 2.

In a first step, S91, an FRM manoeuvre comprising a recruitment phaseand a PEEP titration phase is performed. The PEEP titration phase is aphase of stepwise decrease in PEEP from a maximum PEEP level to aminimum PEEP level, via one or more intermediate PEEP levels.

In a second step, S92, a number of breaths is delivered to the patientat each PEEP level of the PEEP titration phase.

In a third step, S93, a parameter indicative of a potentially harmfullevel of ventilation is monitored during the PEEP titration.

In a fourth and final step, S94, PEEP is automatically decreased to alower PEEP level when the monitored parameter reaches a first thresholdvalue.

The invention claimed is:
 1. A ventilation system, comprising: abreathing apparatus providing a mechanical ventilation to a patient, thebreathing apparatus being configured to perform an automated fullrecruitment manoeuvre, FRM, comprising a recruitment phase and a PEEPtitration phase, wherein the PEEP titration phase is a phase of stepwisedecrease in PEEP from a maximum PEEP level to a minimum PEEP level, viaone or more intermediate PEEP levels, the breathing apparatus beingconfigured to deliver a number of breaths at each PEEP level, and tomonitor a parameter indicative of a potentially harmful level ofventilation during the PEEP titration, the breathing apparatus furtherbeing configured to automatically decrease PEEP to a lower PEEP levelwhen the monitored parameter reaches a first threshold value.
 2. Theventilation system of claim 1, wherein the breathing apparatus isconfigured to decrease PEEP to a lower PEEP level only when themonitored parameter reaches the first threshold value at least for asecond time on a current PEEP level.
 3. The ventilation system of claim1, wherein the breathing apparatus is configured to decrease PEEP to alower PEEP level when the monitored parameter reaches the firstthreshold value for a first time on a current PEEP level only if themonitored parameter has reached the first threshold value duringventilation on any of the preceding PEEP levels.
 4. The ventilationsystem of claim 3, wherein the breathing apparatus is configured todecrease PEEP to a lower PEEP level when the monitored parameter reachesthe first threshold value for at least a second time on a current PEEPlevel even if the monitored parameter has not reached the firstthreshold value during ventilation on any of the preceding PEEP levels.5. The ventilation system of claim 1, wherein the breathing apparatus isconfigured to determine if the monitored parameter reaches a secondthreshold value being lower than the first threshold value during atleast two consecutive breaths, and to decrease PEEP to a lower PEEPlevel if the monitored parameter reaches the second threshold valueduring at least two consecutive breaths.
 6. The ventilation system ofclaim 1, wherein the monitored parameter is indicative of a respiratorypressure of the patient.
 7. A method for lung recruitment in a patientbeing mechanically ventilated by a breathing apparatus, comprising thesteps of: performing an FRM manoeuvre comprising a recruitment phase anda PEEP titration phase, wherein the PEEP titration phase is a phase ofstepwise decrease in PEEP from a maximum PEEP level to a minimum PEEPlevel, via one or more intermediate PEEP levels; delivering a number ofbreaths at each PEEP level; monitoring a parameter indicative of apotentially harmful level of ventilation during the PEEP titration; andautomatically decreasing PEEP to a lower PEEP level based on adetermination that the monitored parameter has reached a first thresholdvalue.
 8. The method of claim 7, wherein the determination that themonitored parameter has reached the first threshold value includesdetermining that the monitored parameter has reached the first thresholdvalue at least for a second time on a current PEEP level.
 9. The methodof claim 7, wherein the determination that the monitored parameter hasreached the first threshold value includes determining that themonitored parameter has reached the first threshold value for a firsttime on a current PEEP level only if the monitored parameter has reachedthe first threshold value during ventilation on any of the precedingPEEP levels.
 10. The method of claim 9, wherein the determination thatthe monitored parameter has reached the first threshold value includesdetermining that the monitored parameter has reached the first thresholdvalue for at least a second time on a current PEEP level even if themonitored parameter has not reached the first threshold value duringventilation on any of the preceding PEEP levels.
 11. The method of claim7, further comprising a steps of: determining that the monitoredparameter has reached a second threshold value being lower than thefirst threshold value during at least two consecutive breaths, anddecreasing PEEP to a lower PEEP level based on the determination thatthe monitored parameter has reached the second threshold value during atleast two consecutive breaths.
 12. The method of claim 7, wherein themonitored parameter is indicative of a respiratory pressure of thepatient.
 13. A computer program product comprising a non-volatile memorystoring a computer program for lung recruitment in a mechanicallyventilated patient, the computer program comprises computer-readableinstruction which, when executed by a computer of a ventilation systemcomprising a breathing apparatus, causes the ventilation system toperform operations, comprising: performing an FRM manoeuvre comprising arecruitment phase and a PEEP titration phase, wherein the PEEP titrationphase is a phase of stepwise decrease in PEEP from a maximum PEEP levelto a minimum PEEP level, via one or more intermediate PEEP levels;deliver a number of breaths at each PEEP level; monitoring a parameterindicative of a potentially harmful level of ventilation during the PEEPtitration; and automatically decreasing PEEP to a lower PEEP level basedon a determination that the monitored parameter has reached a firstthreshold value.